1. Technical Field
This is related to heat transfer devices, and more particularly, to loop heat pipe systems suitable for aerospace use.
2. Description of Related Technology
Two-phase heat transfer systems known as capillary heat pipes and loop heat pipes were first developed in the 1980s. U.S. Pat. No. 4,515,209 to Maidanik et al. describes the first known loop heat pipe, developed in the former Soviet Union in the early 1980s.
The operating temperature of a two-phase heat transfer system is typically governed by the saturation temperature of its compensation chamber. One approach to thermal control has involved cold-biasing the compensating chamber and using an electric heater to maintain the set-point temperature.
For most of the system operational envelope of a typical space-based loop heat pipe system, the heater power is less than about one percent of the total heat transport. However, the heater power increase significantly, e.g., to about 15 to 20%, when the heat sink becomes too hot. For example, in a space environment, a satellite can have a condenser at or near the surface of the satellite. When the side of the satellite having the condenser faces away from the sun, the area is very cold, and the condenser is able to operate effectively. When the side of the satellite having the condenser is facing toward the sun, the heat sink becomes too hot.
To reduce the electrical power expenditure, thermal straps have been used to control the operating temperature, as discussed in J. Ku and H. Nagano, “Loop Heat Pipe Operation with Thermoelectric Converters and Coupling Blocks”, AIAA Paper No. AIAA-2007-4713, pp. 1-14, (2001), and in J. Ku, L. Ottenstein, D. Douglas, Paulken, M., and Birur, G., “Multi-Evaporator Miniature Loop Heat Pipe for Small Spacecraft Thermal Control”, Government Microcircuit Applications and Critical Technology Conference, Las Vegas, NV, Apr. 4-7, 2005.